assuming that \(|\tilde{\rho }| \ll \bar{\rho }\) , \(|\tilde{v}| \ll |\bar{v}|\)  and \(|\tilde{\theta }| \ll \bar{\rho }/q\) .
The linear dispersion can then be found as [1]}, [2]}
\(\omega = k\bar{v} + \frac{\sqrt{\bar{\rho }k}}{\sqrt{\nu k^{2} + 2q}} \left[\frac{\nu k^{2} + 2q}{4\bar{\rho }} k^{3} + 4k \right]^{1/2} .\) 
